JSON Working Group T. Bray, Ed. Internet-Draft Google, Inc. Obsoletes: 4627 (if approved) October08,11, 2013 Intended status: Standards Track Expires: April11,14, 2014 The JSON Data Interchange Formatdraft-ietf-json-rfc4627bis-05draft-ietf-json-rfc4627bis-06 Abstract JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April11,14, 2014. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 1.2. Specifications of JSON . . . . . . . . . . . . . . . . . 3 1.3. Introduction to This Revision . . . . . . . . . . . . . . 31.4. Changes from RFC 4627 . . . . . . . . . . . . . . . . . . 42. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . .54 3. Values . . . . . . . . . . . . . . . . . . . . . . . . . . .64 4. Objects . . . . . . . . . . . . . . . . . . . . . . . . . . .65 5. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . .75 6. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . .76 7. Strings . . . . . . . . . . . . . . . . . . . . . . . . . . .87 8. String and Character Issues . . . . . . . . . . . . . . . . .98 8.1. Encoding and Detection . . . . . . . . . . . . . . . . .98 8.2. Unicode Characters . . . . . . . . . . . . . . . . . . .98 8.3. String Comparison . . . . . . . . . . . . . . . . . . . .109 9. Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . .109 10. Generators . . . . . . . . . . . . . . . . . . . . . . . . .109 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .109 12. Security Considerations . . . . . . . . . . . . . . . . . . .1210 13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . .1210 14. Contributors . . . . . . . . . . . . . . . . . . . . . . . .1311 15. References . . . . . . . . . . . . . . . . . . . . . . . . .1312 15.1. Normative References . . . . . . . . . . . . . . . . . .1312 15.2. Informative References . . . . . . . . . . . . . . . . .1412 Appendix A. Changesin -04 . . . . . . . . . . . . . . . . . . . 14 Appendix B. Changes in -05 . . . .from RFC 4627 . . . . . . . . . . . . . . .1412 Author's Address . . . . . . . . . . . . . . . . . . . . . . . .1514 1. Introduction JavaScript Object Notation (JSON) is a text format for the serialization of structured data. It is derived from the object literals of JavaScript, as defined in the ECMAScript Programming Language Standard, Third Edition [ECMA-262]. JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays). A string is a sequence of zero or more Unicode characters [UNICODE]. An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array. An array is an ordered sequence of zero or more values. The terms "object" and "array" come from the conventions of JavaScript. JSON's design goals were for it to be minimal, portable, textual, and a subset of JavaScript. 1.1. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The grammatical rules in this document are to be interpreted as described in[RFC4234].[RFC5234]. 1.2. Specifications of JSON This document is an update of [RFC4627], which described JSON and registered the Media Type "application/json". A description of JSON in ECMAScript termsfirst appearedappears in version 5.1 of the ECMAScript specification [ECMA-262], section 15.12.It includes a description ofJSON is also described in [ECMA-404]. ECMAscript 5.1 enumerates the differences between JSON as described in that specification and in RFC4627. The most significant is that ECMAScript 5.1 does not require a JSON Text to be an Array or an Object; thus, for example,"Hello world!", "42", and "true"these constructs would all be valid JSON texts in the ECMAScript5.1 context. JSON is also described in [ECMA-404]. Nonecontext: o "Hello world!" o 42 o true All of the specifications of JSON syntaxdisagreeagree on thesyntaxsyntactic elements of the language. 1.3. Introduction to This Revision In the years since the publication of RFC 4627, JSON has found very wide use. This experience has revealed certain patterns which, while allowed by its specifications, have caused interoperability problems. Also, a small number of errata have been reported. This revision does not change any of the rules of the specification; all texts which were legal JSON remain so, and none which were not JSON become JSON. The revision's goal is to fix the errata and highlight practices which can lead to interoperability problems.1.4. Changes from RFC 4627 This section lists all changes between this document and the text in RFC 4627. o Changed Working Group attribution to JSON Working Group. o Changed title of document. o Change the reference to [UNICODE] to be be non-version-specific. o Added a "Specifications of JSON" section. o Added an "Introduction to this Revision" section. o Added language about duplicate object member names and interoperability. o Applied erratum #607 from RFC 4627 to correctly align the artwork for the definition of "object". o Changed "as sequences of digits" to "in the grammar below" in "Numbers" section. o Added language about number interoperability as a function of IEEE754, and an IEEE754 reference. o Added language about interoperability and Unicode characters, and about string comparisons. To do this, turned the old "Encoding" section into a "String and Character Issues" section, with three subsections: The old "Encoding" material, and two new sections for "Unicode Characters" and "String Comparison". o Changed guidance in "Parsers" section to point out that implementations may set limits on the range "and precision" of numbers. o Removed the language "Interoperability considerations: n/a" from the "IANA Considerations" section. o Made a real "Security Considerations" section, and lifted the text out of the existing "IANA Considerations" section. o Applied erratum #3607 from RFC 4627 by removing the security consideration that begins "A JSON text can be safely passed" and the JavaScript code that went with that consideration. o Added a note to the "Security Considerations" section pointing out the risks of using the "eval()" function in JavaScript or any other language in which JSON texts conform to that language's syntax. o Added "Contributors" section crediting Douglas Crockford. o Moved the ECMAScript reference from Normative to Informative, updated it to reference ECMAScript 5.1, and added reference to ECMA 404.2. JSON Grammar A JSON text is a sequence of tokens. The set of tokens includes six structural characters, strings, numbers, and three literal names. A JSON text is a serialized object or array. JSON-text = object / array These are the six structural characters: begin-array = ws %x5B ws ; [ left square bracket begin-object = ws %x7B ws ; { left curly bracket end-array = ws %x5D ws ; ] right square bracket end-object = ws %x7D ws ; } right curly bracket name-separator = ws %x3A ws ; : colon value-separator = ws %x2C ws ; , comma Insignificant whitespace is allowed before or after any of the six structural characters. ws = *( %x20 / ; Space %x09 / ; Horizontal tab %x0A / ; Line feed or New line %x0D ) ; Carriage return)3. Values A JSON value MUST be an object, array, number, or string, or one of the following three literal names: false null true The literal names MUST be lowercase. No other literal names are allowed. value = false / null / true / object / array / number / string false = %x66.61.6c.73.65 ; false null = %x6e.75.6c.6c ; null true = %x74.72.75.65 ; true 4. Objects An object structure is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members). A name is a string. A single colon comes after each name, separating the name from the value. A single comma separates a value from a following name. The names within an object SHOULD be unique. object = begin-object [ member *( value-separator member ) ] end-object member = string name-separator value An object whose names are all unique is interoperable in the sense that all software implementations which receive that object will agree on the name-value mappings. When the names within an object are not unique, the behavior of software that receives such an object is unpredictable. Many implementations report the last name/value pair only; other implementations report an error or fail to parse the object; other implementations report all of the name/value pairs, including duplicates. 5. Arrays An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas. array = begin-array [ value *( value-separator value ) ] end-array 6. Numbers The representation of numbers is similar to that used in most programming languages. A number contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Octal and hex forms are not allowed. Leading zeros are not allowed. A fraction part is a decimal point followed by one or more digits. An exponent part begins with the letter E in upper or lowercase, which may be followed by a plus or minus sign. The E and optional sign are followed by one or more digits. Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted. number = [ minus ] int [ frac ] [ exp ] decimal-point = %x2E ; . digit1-9 = %x31-39 ; 1-9 e = %x65 / %x45 ; e E exp = e [ minus / plus ] 1*DIGIT frac = decimal-point 1*DIGIT int = zero / ( digit1-9 *DIGIT ) minus = %x2D ; - plus = %x2B ; + zero = %x30 ; 0 This specification allows implementations to set limits on the range and precision of numbers accepted. Since software which implements IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is generally available and widely used, good interoperability can be achieved by implementations which expect no more precision or range thanprovided by an IEEE 754 binary64 (double precision) number,these provide, in the sense that implementations will approximate JSON numbers within the expected precision. A JSON numberwhich is outside those bounds,such as 1E400 or3.141592653589793238462643383279,3.141592653589793238462643383279 may indicate potential interoperability problems since it suggests that the software which created it it expected greater magnitude or precision than is widely available. Note that when such software is used, numbers which are integers and are in the range [-(2**53)+1, (2**53)-1] are interoperable in the sense that implementations will agree exactly on their numeric values. 7. Strings The representation of strings is similar to conventions used in the C family of programming languages. A string begins and ends with quotation marks. All Unicode characters may be placed within the quotation marks except for the characters that must be escaped: quotation mark, reverse solidus, and the control characters (U+0000 through U+001F). Any character may be escaped. If the character is in the Basic Multilingual Plane (U+0000 through U+FFFF), then it may be represented as a six-character sequence: a reverse solidus, followed by the lowercase letter u, followed by four hexadecimal digits that encode the character's code point. The hexadecimal letters A though F can be upper or lowercase. So, for example, a string containing only a single reverse solidus character may be represented as "\u005C". Alternatively, there are two-character sequence escape representations of some popular characters. So, for example, a string containing only a single reverse solidus character may be represented more compactly as "\\". To escape an extended character that is not in the Basic Multilingual Plane, the character is represented as a twelve-character sequence, encoding the UTF-16 surrogate pair. So, for example, a string containing only the G clef character (U+1D11E) may be represented as "\uD834\uDD1E". string = quotation-mark *char quotation-mark char = unescaped / escape ( %x22 / ; " quotation mark U+0022 %x5C / ; \ reverse solidus U+005C %x2F / ; / solidus U+002F %x62 / ; b backspace U+0008 %x66 / ; f form feed U+000C %x6E / ; n line feed U+000A %x72 / ; r carriage return U+000D %x74 / ; t tab U+0009 %x75 4HEXDIG ) ; uXXXX U+XXXX escape = %x5C ; \ quotation-mark = %x22 ; " unescaped = %x20-21 / %x23-5B / %x5D-10FFFF 8. String and Character Issues 8.1. Encoding and Detection JSON text SHALL be encoded in Unicode. The default encoding is UTF-8. Since the first two characters of a JSON text will always be ASCII characters [RFC0020], it is possible to determine whether an octet stream is UTF-8, UTF-16 (BE or LE), or UTF-32 (BE or LE) by looking at the pattern of nulls in the first four octets. 00 00 00 xx UTF-32BE 00 xx 00 xx UTF-16BE xx 00 00 00 UTF-32LE xx 00 xx 00 UTF-16LE xx xx xx xx UTF-8 8.2. Unicode Characters When all the strings represented in a JSON text are composed entirely of Unicode characters [UNICODE] (however escaped), then that JSON text is interoperable in the sense that all software implementations which parse it will agree on the contents of names and of string values in objects and arrays. However, the ABNF in this specification allows member names and string values to contain bit sequences which cannot encode Unicode characters, for example "\uDEAD" (a single unpaired UTF-16 surrogate). Instances of this have been observed, for example when a library truncates a UTF-16 string without checking whether the truncation split a surrogate pair. The behavior of software which receives JSON texts containing such values is unpredictable; for example, implementations might return different values for the length of a string value, or even suffer fatal runtime exceptions. 8.3. String Comparison Software implementations are typically required to test names of object members for equality. Implementations which transform the textual representation into sequences of Unicode code units, and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations which compare strings with escaped characters unconverted may incorrectly find that "a\b" and "a\u005Cb" are not equal. 9. Parsers A JSON parser transforms a JSON text into another representation. A JSON parser MUST accept all texts that conform to the JSON grammar. A JSON parser MAY accept non-JSON forms or extensions. An implementation may set limits on the size of texts that it accepts. An implementation may set limits on the maximum depth of nesting. An implementation may set limits on the range and precision of numbers. An implementation may set limits on the length and character contents of strings. 10. Generators A JSON generator produces JSON text. The resulting text MUST strictly conform to the JSON grammar. 11. IANA Considerations The MIME media type for JSON text is application/json. Type name: application Subtype name: json Required parameters: n/a Optional parameters: n/a Encoding considerations: 8bit if UTF-8; binary if UTF-16 orUTF-32UTF-32. JSON may be represented using UTF-8, UTF-16, or UTF-32. When JSON is written in UTF-8, JSON is 8bit compatible. When JSON is written in UTF-16 or UTF-32, the binary content-transfer-encoding must be used. Interoperability considerations: Described in this document Published specification:RFC 4627This document Applications that use this media type: JSON has been used to exchange data between applications written in all of these programming languages: ActionScript, C, C#, Clojure, ColdFusion, Common Lisp, E, Erlang, Go, Java, JavaScript, Lua, Objective CAML, Perl, PHP, Python, Rebol, Ruby, Scala, and Scheme. Additional information: Magic number(s): n/a File extension(s): .json Macintosh file type code(s): TEXT Person & email address to contact for further information:Douglas Crockford douglas@crockford.comIESG <iesg@ietf.org Intended usage: COMMON Restrictions on usage: none Author: Douglas Crockford douglas@crockford.com Change controller:Douglas Crockford douglas@crockford.comIESG <iesg@ietf.org 12. Security Considerations Generally there are security issues with scripting languages. JSON is a subset of JavaScript, but excludes assignment and invocation. Since JSON's syntax is borrowed from JavaScript, it is possible to use that language's "eval()" function to parse JSON texts. This generally constitutes an unacceptable security risk, since the text could contain executable code along with data declarations. The same consideration applies in any other programminglanguageslanguage in which JSON texts conform to that language's syntax. 13. Examples This is a JSON object: { "Image": { "Width": 800, "Height": 600, "Title": "View from 15th Floor", "Thumbnail": { "Url": "http://www.example.com/image/481989943", "Height": 125, "Width":"100"100 }, "Animated" : false, "IDs": [116, 943, 234, 38793] } } Its Image member is an object whose Thumbnail member is an object and whose IDs member is an array of numbers. This is a JSON array containing two objects: [ { "precision": "zip", "Latitude": 37.7668, "Longitude": -122.3959, "Address": "", "City": "SAN FRANCISCO", "State": "CA", "Zip": "94107", "Country": "US" }, { "precision": "zip", "Latitude": 37.371991, "Longitude": -122.026020, "Address": "", "City": "SUNNYVALE", "State": "CA", "Zip": "94085", "Country": "US" } ] 14. Contributors RFC 4627 was written by Douglas Crockford. This document was constructed by making a relatively small number of changes to that document; thus the vast majority of the text here is his. 15. References 15.1. Normative References [IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", 2008, <http://grouper.ieee.org/groups/754/>. [RFC0020] Cerf, V., "ASCII format for network interchange", RFC 20, October 1969. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.[RFC4234][RFC5234] Crocker,D., Ed.D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC4234, October 2005.5234, January 2008. [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 4.0 ", 2003, <http://www.unicode.org/versions/latest/>. 15.2. Informative References [ECMA-262] European Computer Manufacturers Association, "ECMAScript Language Specification 5.1 Edition ", June 2011, <http:// www.ecma-international.org/ecma-262/5.1/>. [ECMA-404] Ecma International, "The JSON Data Interchange Format ", October 2013, <http://www.ecma-international.org/ publications/standards/Ecma-404.htm>. [RFC4627] Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, July 2006. Appendix A. Changesin -04 o Reworded Section 8.2 to talk about strings that are represented in the JSON text, rather thanfrom RFC 4627 This section lists changes between this document and theactualtextitself. Also fine- tuned the "will agree on" clauseinthe interoperability description.RFC 4627. o Changed"20008"Working Group attribution to"2008".JSON Working Group. oReworded numeric-interoperability language following on WG discussion, notably referring to availabilityChanged title ofsoftware that does IEEE754 and "approximate JSON numbers withindocument. o Change theexpected precision". Also took out duplicatereference to [UNICODE] to be be non-version-specific. o Added a "Specifications of JSON" section. o Added an "Introduction to this Revision" section. o Added language aboutNaNduplicate object member names andInf.interoperability. o Applied erratum #607 from RFC 4627 to correctly align the artwork for the definition of "object". o Changed "as sequences of digits" to "in the grammar below" in "Numbers" section.Appendix B. Changes in -05oRemoved the numbers-interop textAdded language about"frac"number interoperability as a function of IEEE754, and"exp" parts.an IEEE754 reference. o Added language about interoperability and Unicode characters, and about string comparisons. To do this, turned theobsoletes 4627 attribute. o Moved the EcmaScript ref from normative to informative,old "Encoding" section into a "String andredirected to point at 5.1.Character Issues" section, with three subsections: The old "Encoding" material, and two new sections for "Unicode Characters" and "String Comparison". o Changednumbers languageguidance in "Parsers" section tosaypoint out that implementationscan imposemay set limits on the range*and precision*."and precision" of numbers. oChanged section title from "Character Model" to "StringUpdated andCharacter Issues".tidied the "IANA Considerations" section. oAdded "Specifications of JSON"Made a real "Security Considerations" section, andincluded a reference to ECMA-404. o Removedlifted the text out of theconsensus-call linkexisting "IANA Considerations" section. o Applied erratum #3607 from RFC 4627 by removing thelist of changes.security consideration that begins "A JSON text can be safely passed" and the JavaScript code that went with that consideration. o Added aparagraph about notnote to the "Security Considerations" section pointing out the risks of usingeval()the "eval()" function in JavaScript or any otherlanguaegs wherelanguage in which JSONsyntax matchestexts conform to that language's syntax. oReorganizedChanged "100" to 100 and added a boolean field, both in thelist of changes so they're ordered likefirst example. o Added "Contributors" section crediting Douglas Crockford. o Added a reference to RFC4627. o Moved thespec,ECMAScript reference from Normative to Informative, updated it to reference ECMAScript 5.1, andcleaned up language a bit.added reference to ECMA 404. Author's Address Tim Bray (editor) Google, Inc. Email: tbray@textuality.com